Scanning electron microscope

A scanning electron microscope comprising:

• an electron lens for converging an electron beam emitted from an electron source onto a specimen;
• a pair of first and second detectors and a third detector for detecting secondary signals from said specimen when irradiated with said electron beam, said first and second detectors being provided to be spaced from each other by a predetermined spacing;
• a storage unit for generating and storing first, second and third pieces of secondary signal data from the secondary signals detected by said first, second and third detectors at respective focuses, said focuses of said electron beam to said specimen are changed a plurality of times;
• a data calculation unit for performing combining operation to combine said first, second and third pieces of secondary signal data at the respective focuses;
• and
• a focus adjustment unit for calculating an evaluation value based on an intensity signal obtained by subjecting said combined secondary signal data at the focuses to predetermined data conversion, and adjusting a focus of said electron beam to said specimen using the focuses calculated based on said evaluation values for the focuses,
• wherein said combining operation is carried out by adding differences between said first secondary signal data and said second secondary signal data corresponding to the respective focuses to said third secondary signal data at the focuses at a predetermined ratio.

A scanning electron microscope comprising:

• an electron lens for converging an electron beam emitted from an electron source onto a specimen;
• a pair of first and second detectors and a third detector for detecting secondary signals from said specimen when irradiated with said electron beam, said first and second detectors being provided to be spaced from each other by a predetermined spacing;
• a storage unit for generating and storing first, second and third pieces of secondary signal data from the secondary signals detected by said first, second and third detectors at respective focuses, said focuses of said electron beam to said specimen are changed a plurality of times;
• a data calculation unit for performing combining operation to combine said first, second and third pieces of secondary signal data at the respective focuses;
• and
• a focus adjustment unit for calculating an evaluation value based on an intensity signal obtained by subjecting said combined secondary signal data at the focuses to predetermined data conversion, and adjusting a focus of said electron beam to said specimen using the focuses calculated based on said evaluation values for the focuses,
• wherein said focus adjustment unit applies differentiating operation to said combined secondary signal data at the respective focuses to calculate pixel values, calculates an evaluation value based on a sum of the pixel values, and adjusts the focus of said electron beam to said specimen using the focus calculated based on maximum one of the evaluation values.

A scanning electron microscope comprising:

• an electron lens for converging an electron beam emitted from an electron source onto a specimen;
• a pair of first and second detectors and a third detector for detecting secondary signals from said specimen when irradiated with said electron beam, said first and second detectors being provided to be spaced from each other by a predetermined spacing;
• a storage unit for generating and storing first, second and third pieces of secondary signal data from the secondary signals detected by said first, second and third detectors at respective focuses, said focuses of said electron beam to said specimen are changed a plurality of times;
• a data calculation unit for performing combining operation to combine said first, second and third pieces of secondary signal data at the respective focuses;
• and
• a focus adjustment unit for calculating an evaluation value based on an intensity signal obtained by subjecting said combined secondary signal data at the focuses to predetermined data conversion, and adjusting a focus of said electron beam to said specimen using the focuses calculated based on said evaluation values for the focuses,
• wherein said focus adjustment unit applies differentiating operation to the combined secondary signal data at the focuses to calculate pixel values, calculates an evaluation value based on a sum of the pixel values, determines a fitting function followed by the evaluation values, and adjusts the focus of said electron beam to said specimen using a focus providing a peak value to the fitting function.

A scanning electron microscope comprising:

• an electron lens for converging an electron beam emitted from a electron source onto a specimen;
• a pair of first and second detectors and a third detector for detecting secondary signals from said specimen when irradiated with said electron beam, said first and second detectors being provided to be spaced from each other by a predetermined distance;
• a storage unit for generating and storing first, second and third secondary signal data from the secondary signals detected by said first, second and third detectors at respective focuses, and said focuses of said electron beam to said specimen are changed a plurality of times;
• a data calculation unit for calculating said first, second and third secondary signal data at the respective focuses;
• an input unit for externally receiving data necessary for the calculating operation of said data calculation unit;
• an image display unit for displaying a command menu and indicating input data from said input unit as a result of said calculating operation executed by said data calculation unit and indicating contents of said calculating operation executed by said data calculation unit;
• a focus adjustment unit for calculating an evaluation value on the basis of an intensity signal obtained by applying predetermined conversion to secondary signal data at the focuses executed and calculated by said data calculation unit, and adjusts the focus of said electron beam to said specimen using the focuses based on said evaluation values corresponding to the focuses, wherein:
• said calculating operation of said data calculation unit is carried out by combining said first, second and third secondary signal data at the focus of said electron beam according to a preset equation, and
• data for modifying coefficients preset in said equation are input from said input unit.

A scanning electron microscope comprising:

• an electron lens for converging an electron beam emitted from an electron source onto a specimen;
• a pair of first and second detectors and a third detector for detecting secondary signals from said specimen when irradiated with said electron beam, said first, second and third detectors being provided to be spaced in each pair from each other by a predetermined spacing;
• a storage unit for generating and storing first, second and third pieces of secondary signal data from the secondary signals detected by said first, second and third detectors for respective focuses of said electron beam to said specimen changed by a plurality of times;
• a data calculation unit for calculating said first, second and third pieces of secondary signal data at the respective focuses;
• a detector selection unit for detecting at least any one of said first, second and third detectors;
• and
• a focus adjustment unit for generating secondary signal data from the detector selected by said detector selection unit by changing the focus of said electron beam, calculating an evaluation value of the secondary signal data for the respective focuses changed based on intensity signals obtained by subjecting the generated secondary signal data to predetermined data conversion, determining a fitting function corresponding to the evaluation value, calculating an error between the evaluation value and said fitting function, adjusting the focus of said electron beam to said specimen using a focus giving a peak value to said fitting function when the error is in a predetermined reference range, selecting the detector different from the detector selected by the detector selection unit when the error is out of the predetermined reference range, calculating an error between the evaluation value and the fitting function with respect to the different detector, and adjusting the focus of said electron beam to said specimen using focuses having the errors lying in the predetermined reference range.